Manage Add-Ons button is where you can add these following services below on top of your base plan.

Click on Manage Add-Ons button

Select the plan which you are currently subscribed on.

Click Edit Subscription

Click Add Addons button

Select the addons you want to apply in your account and hit Add button.

You can view your updated Billing Invoices following this link below.
​Access your Billing Invoices